The present invention generally relates to turbine flowmeters, and more particularly to a turbine flowmeter having such a construction that a rotary shaft of an impeller can be supported stably for a long period of time.
Conventionally, in a turbine flowmeter for measuring a flow quantity of a fluid such as a gas supplied through a gas pipe arrangement, a pair of pivot bearings support respective ends of a rotary shaft projecting from both sides of a hub of an impeller. In order to improve the measuring accuracy of the turbine flowmeter especially at the start of the measuring operation, two cone shaped members are respectively provided on an upstream side and a downstream side of the hub of the impeller so as to confront the two sides of the hub, and the pivot bearings are provided within the two cone shaped members. The two ends of the rotary shaft respectively have a conical shape, and a bearing surface of each pivot bearing has a hemispherical shape in correspondence with the conical ends of the rotary shaft.
However, in the bearing parts of the conventional turbine flowmeter, the rotary shaft rotates on the bearing surfaces of the pivot bearings together with the impeller when measuring the flow quantity of the fluid. For this reason, a large force acts on the bearing surfaces from the rotary shaft. As a result, both the bearing surfaces and the ends of the rotary shaft wear out due to friction after the turbine flowmeter is used for a certain period of time, and there is a problem in that the durability of the pivot bearings and the rotary shaft is unsatisfactory.
In order to solve the problem of wear due to friction, it is possible to conceive a method of accumulating a lubricating oil on the bearing surfaces. But when the quantity of the lubricating oil is too small, the lubrication is insufficient. On the other hand, the lubricating oil acts as a resistance on the rotating rotary shaft when the quantity of the lubricating oil is too large. Therefore, when the quantity of the lubricating oil is too large, there are problems in that the measuring accuracy of the turbine flowmeter becomes poor, and the excess lubricating oil is scattered to the surroundings of the bearing parts.